Field of the Invention
This invention relates to flame and smoke barriers. More particularly, this invention relates to intumescent compositions useful as flame and smoke barriers in passages traversing partitions such as walls and floors. The passages are occupied by thermoplastic articles such as pipes and conduits that undergo a decrease in external dimensions when exposed to flame temperatures.
Recent modifications in building codes permit the use of pipes, conduits and other articles formed from thermoplastic materials such as polyvinyl chloride. The advantages of such articles are their lower material and installation costs relative to the same articles fabricated from metals. These economic advantages can be more than offset by the flammability and relatively low melting point of many commonly used thermoplastic materials. In the event of a fire in an area where articles such as pipes and/or conduits formed from thermoplastic or other heat sensitive materials pass through a partition such as a wall or floor, these materials melt and create an opening in the partition through which flames and smoke can spread to the area on the other side of the partition.
It is known to seal passages in partitions that are traversed by pipes, conduits and electrical cables using foamable polyorganosiloxane compositions such as those disclosed in U.S. Pat. No. 3,923,705, which issued to Smith on Dec. 2, 1975. This patent teaches preparing foams by blending an organohydrogensiloxane, a hydroxylated organosiloxane and a platinum catalyst in amounts such that the ratio of silicon-bonded hydrogen atoms to silicon-bonded hydroxyl radicals is from 2.5 to 40. The composition can optionally include a vinyl containing triorganosiloxy terminated polydiorganosiloxane and carbon black as a flame retarding agent.
U.S. Pat. No. 4,433,069, which issued to Harper on Feb. 21, 1984 discloses adding fibrous and particulate materials to foamable compositions of the aforementioned Smith patent to decrease the rate of burn-through. A disadvantage of foams prepared using compositions described in the Smith and Harper patents is that when these foams are installed around thermoplastic articles that melt or decompose when exposed to the intense heat generated by a fire, the foams usually cannot expand sufficiently to fill the resultant void, and thereby cease functioning as a fire and smoke barrier.
U.S. Pat. No. 3,983,082, which issued to Pratt et al on Sept. 28, 1976, relates to intumescent silicone resin compositions containing (1) a mixture of iron oxide and potassium phosphate, which decompose at flame temperatures to produce a crust, (2) a char - forming material such as tripentaerythritol and (3) a heat activated blowing agent such as a melamine compound. The compositions are intended for use as coatings on relatively thin substrates such as the supporting members of gas turbine engines to protect the substrates from burning through in the event of a fire. If the compositions were used to fill passages occupied by heat sensitive articles, the crusty, brittle shell that functions as an effective heat insulator would not allow the composition to expand sufficiently to fill the void remaining following shrinkage and/or collapse of the thermoplastic article.
The prior art discloses foamable, elastomeric polyorganosiloxane compositions wherein the agent responsible for formation of the foam is an organic compound that decomposes when heated to produce a gas. If a composition of this type were evaluated as a fire barrier by placing it in a relatively narrow passage traversed by at least one hollow thermoplastic article and subsequently exposing the composition to the intense heat generated by a fire, substantially all of the available gas would be liberated when the temperature within the passage reached the decomposition temperature of the blowing agent. Once this occurred, there would be only a relatively limited capability for additional expansion to compensate for subsequent void formation resulting from the collapse of thermoplastic articles within the passage. Foamable compositions containing only chemical blowing agents would therefore be unsuitable for use as fire and smoke barriers under these conditions.
An additional disadvantage of using a chemical blowing agent in the relatively narrow confines of a passage traversing a partition is rupturing of the cell walls of the foam or complete disintegration of the cellular structure due to the pressure resulting from the gas generated during a rapid decomposition of the blowing agent. The cured product could not function as a fire or smoke barrier.
Canadian Pat. No. 715,140, which issued on Aug. 3, 1965, teaches a method for producing closed cell sponge rubber by blending gas filled thermoplastic microspheres into an uncured or partially cured rubber formulation, shaping the resultant composition into the desired form using conventional fabricating means and then heating the composition while allowing it to expand in the desired directions to form the final foam product. Silicones, a commercially accepted nomenclature for polyorganosiloxane elastomers, are one of the many classes of rubbers considered suitable for use with the disclosed method. This patent does not disclose expansion of previously cured foams or using either foamable compositions or cured foams containing gas-filled microspheres as fire and smoke barriers.
U.S. Pat. No. 4,433,022 discloses three-dimensional decorative facings for ceiling and wall boards. The facings are formed by applying a paste or plastisol to selected areas of a fabric adhered to a ceiling or wall board and subsequently heating to expand the material. The agents responsible for the expansion pastes and plastisols are hollow, microspheres having a shell formed from a thermoplastic synthetic resin and containing a volatile organic liquid that boils below the glass transition temperature of the resin. When the microspheres are heated the pressure generated by volatilization of the liquid causes expansion of the particle to form a monocellular, generally spherical shell containing the volatilized liquid entrapped therein.
The teaching of this patent is limited to use of the certain expandable pastes and plastisols as coating materials. There is no suggestion of incorporating the disclosed liquid filled microspheres into polyorganosiloxane compositions suitable for preparing self supporting foams or the utility of such foams as fire and smoke barriers.
An objective of this invention is to provide intumescent compositions suitable for use as fire and smoke barriers in conjunction with thermoplastic articles.
Under the intense heat generated by a fire the present compositions expand to fill voids created by shrinkage and/or collapse of adjacent hollow thermoplastic articles while maintaining the structural integrity of the barrier.